Parse JSON file in Java: getJSONObject(int) is undefined

Question

I`m trying to fetch some values fron a JSON file using:

JSONParser parser = new JSONParser();
Object obj = parser.parse(new FileReader("C:\\myfile.json"));
JSONArray array= new JSONArray();
array.add(obj);

If I run: System.out.println(array); , the output is

[{"flowrate":{"mod":0,"value":110},"command":{"cancel":0,"start":0}}]

, which is my json file. My problem is how to get value from a specific field, let's say the value of "comand":"cancel".

I've tried JSONObject myitem = array.getJSONObject(1).getJSONObject("cancel"); with no success (error: getJSONObject(int) is undefined for the type JSONArray).

I mention that I'm using the json-simple toolkit.

I tried validating the JSON you're using at jsonlint.com and it says it's not valid. Is "["flowrate":{"mod":0,"value":110},"command":{"cancel":0,"start":0}] " the JSON that's in your myfile.json? — Shane Sepac
– Shane Sepac, Commented Apr 22, 2018 at 15:43
you are right. My mistake that i kind of wrote it from memory. it was missing { } final enclosure — s.dragos
– s.dragos, Commented Apr 22, 2018 at 15:53

RBH · Accepted Answer · 2018-04-22 16:05:22Z

1

I also could not validate your JSON. I made an assumption that you wanted to create an array of two objects (flowrate and command) and fixed the JSON:

    String value = "[{\"flowrate\":{\"mod\":0,\"value\":110}},{\"command\":{\"cancel\":0,\"start\":0}}]";
    JSONParser parser = new JSONParser();
    Object obj = parser.parse(value);
    JSONArray array=(JSONArray)obj;
    JSONObject jo = (JSONObject) array.get(1);
    System.out.println(jo.get("command"));

which gives the following output:

{"cancel":0,"start":0}

Process finished with exit code 0

answered Apr 22, 2018 at 16:05

RBH

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1 Comment

s.dragos Over a year ago

your example works, but i still can't understand why the same stupid json refuses to work when it is parsed from file. man, it gets frustrating :))

s.dragos · Accepted Answer · 2018-04-22 18:17:35Z

0

After many hours of searching, I discovered that there is big difference between { } and [ ], therefore differnent methodes to parse them:

In my case:

JSONParser parser = new JSONParser();
Object obj = parser.parse(new FileReader("C:\\myfile.json"));
JSONObject jsonObject =  (JSONObject) json;
JSONObject command= (JSONObject) jsonObject.get("command");
System.out.println("command: " + command);
long cancel= (Long) command.get("cancel");
System.out.println("cancel: " + cancel);

Here you'll find the best example for nested json objects

answered Apr 22, 2018 at 18:17

s.dragos

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